function addrain() {
    // viewer.shadowMap.darkness = 0.9; //阴影强度
    let collection = viewer.scene.postProcessStages;
    let snow = new Cesium.PostProcessStage({
        name: 'czm_rain',
        fragmentShader: `
            uniform sampler2D colorTexture;//输入的场景渲染照片
            varying vec2 v_textureCoordinates;
            uniform float vrain;

            float hash(float x){
                return fract(sin(x*133.3)*13.13);
            }

            void main(void){
                float time = czm_frameNumber / vrain;
                vec2 resolution = czm_viewport.zw;
                
                vec2 uv=(gl_FragCoord.xy*2.-resolution.xy)/min(resolution.x,resolution.y);
                vec3 c=vec3(.6,.7,.8);
                float a=0.4;
                float si=sin(a),co=cos(a);
                uv*=mat2(co,-si,si,co);
                uv*=length(uv+vec2(0,4.9))*.3+1.;
                
                float v=1.-sin(hash(floor(uv.x*100.))*2.);
                float b=clamp(abs(sin(20.*time*v+uv.y*(5./(2.+v))))-.95,0.,1.)*20.;
               
                c*=v*b; //屏幕上雨的颜色
                gl_FragColor = mix(texture2D(colorTexture, v_textureCoordinates), vec4(c,1), 0.5); //将雨和三维场景融合
            }
        `,
        uniforms: {
            vrain: function() {
                return 200 //value:时间
            }
        }
    });
    collection.add(snow);
}

function addsnow() {
    // viewer.shadowMap.darkness = 0.9; //阴影强度
    let collection = viewer.scene.postProcessStages;
    let snow = new Cesium.PostProcessStage({
        name: 'czm_snow',
        fragmentShader: `
            uniform sampler2D colorTexture;
            varying vec2 v_textureCoordinates;
            uniform float vsnow;
            
            float snow(vec2 uv,float scale)
            {   float time = czm_frameNumber / vsnow;
                float w=smoothstep(1.,0.,-uv.y*(scale/10.));if(w<.1)return 0.;
                uv+=time/scale;uv.y+=time*2./scale;uv.x+=sin(uv.y+time*.5)/scale;
                uv*=scale;vec2 s=floor(uv),f=fract(uv),p;float k=3.,d;
                p=.5+.35*sin(11.*fract(sin((s+p+scale)*mat2(7,3,6,5))*5.))-f;d=length(p);k=min(d,k);
                k=smoothstep(0.,k,sin(f.x+f.y)*0.01);
                return k*w;
            }
            void main(void){
                vec2 resolution = czm_viewport.zw;
                vec2 uv=(gl_FragCoord.xy*2.-resolution.xy)/min(resolution.x,resolution.y);
                vec3 finalColor=vec3(0);
                float c = 0.0;
                c+=snow(uv,30.)*.0;
                c+=snow(uv,20.)*.0;
                c+=snow(uv,15.)*.0;
                c+=snow(uv,10.);
                c+=snow(uv,8.);
                c+=snow(uv,6.);
                c+=snow(uv,5.);
                finalColor=(vec3(c));
                gl_FragColor = mix(texture2D(colorTexture, v_textureCoordinates), vec4(finalColor,1), 0.5);
            }
        `,
        uniforms: {
            vsnow: function() {
                return 60 //value:时间，其他为固定值
            }
        }
    });
    collection.add(snow);
}

function addfog() {
    let fogthicknessnum = 1.0; //可见度
    let collection = viewer.scene.postProcessStages;
    let fogfragmentShader = `uniform sampler2D colorTexture;uniform sampler2D depthTexture;varying vec2 v_textureCoordinates;uniform float fognum;void main(void){vec4 origcolor=texture2D(colorTexture, v_textureCoordinates);vec4 fogcolor=vec4(0.8,0.8,0.8,0.5);float depth = czm_readDepth(depthTexture, v_textureCoordinates);vec4 depthcolor=texture2D(depthTexture, v_textureCoordinates);float f=(depthcolor.r-0.22)/fognum;if(f<0.0) f=0.0;else if(f>1.0) f=1.0;gl_FragColor = mix(origcolor,fogcolor,f);}`;
    let fog = new Cesium.PostProcessStage({
        fragmentShader: fogfragmentShader,
        uniforms: {
            scale: 1.1,
            offset: function() {
                return new Cesium.Cartesian3(0.1, 0.2, 0.3);
            },
            fognum: () => {
                return fogthicknessnum;
            },
        },
    })
    collection.add(fog);

}

function closeWeather() {
    viewer.scene.postProcessStages.removeAll();
}
